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Marine experts believe the mass mortality has been caused by harmful algal bloom
- Tuesday, August 27, 2013 - From Print Edition




Something’s terribly wrong at the seashore. For the second time within a month, a large number of dead fish have washed ashore in Karachi


While the quantity of fish is quite small as compared to the last time, fisheries’ experts believe the mass killing this time has been caused by “red tide” – a natural phenomenon which occurs due to the immense growth of marine algae usually in coastal waters.


Red tides, locally termed “mara paani” (in Sindhi) and “bad aab” (in Baloch language), can produce natural toxins or deplete dissolved oxygen, resulting in the death of marine and coastal species of fish and even sometimes birds and marine mammals.


On August 5, around 100 metric tonnes of dead fish, mainly grey mullets, had washed ashore on the beaches of Karachi between Baba Island and Chinna Creek. The mortalities were attributed to the toxic rainwater flowing in the sea from Lyari River, which flows through the industrial areas.


This time, a small quantity of dead fish, including tigertooth croaker, mullets, terapons, scat and seabreams, have been beaching in patches along the Clifton beach since Saturday.


While the dead fish have been attributed to red tide, the reason for the sudden growth of algae is not well understood, experts at World Wide Fund for Nature-Pakistan (WWF) said on Monday.


“But the recurring mortality of natural fish stocks may severely affect the livelihood of the fishermen in the coastal areas,” pointed out WWF-Pakistan Director Rab Nawaz.Fish deaths on account of toxic phytoplankton can be widespread and direct or indirect consumption of such organisms can be harmful for humans.


The WWF-Pakistan has collected samples of the dead fish for analysis to identify the species of phytoplankton causing mass mortality.Moazzam Khan, the marine fisheries technical adviser at WWF-Pakistan, said abrupt growth of toxic phytoplankton was known as “harmful algal bloom”.


Phytoplankton is not harmful to humans and marine animals. But owing to a number of reasons, some of which are still not well understood, these algae grow in millions changing the colour of the water ranging from green to blood red.


Red tides are a regular occurrence in Pakistani waters often resulting in mass mortality of fish. Khalid Mahmood, the co-principal investigator, and Saba Ayub, the data enumerator at WWF-Pakistan, who surveyed the area pointed out that fish mortality was widespread along the entire Clifton coast, mainly at Do Darya and Sea View but the quantities were not large.


Most of the dead fish have already been collected for fish meal processors. Khan was concerned that use of such fish for fish meal and human consumption could lead to serious health issues.


He pointed out the WWF-Pakistan was working with the National Institute of Oceanography to identify the species of phytoplankton responsible for fish mortality. The first such record in Pakistani waters dates back to the 13th century. A red tide in 1906 resulted in the elimination of the entire stock of oysters from waters of Sindh.


The WWF-Pakistan has urged research organisations to keep an eye on the appearance of harmful algal blooms and set up a regular monitoring system as some of these blooms can be harmfully toxic and may lead to serious health issues.